For the Wind Energy Conversion System, when the sensors and the actuators are error, according to multi-time scale of wind speed, two-frequency-loop model is established for WECS based on the nonlinear mechanical model. According to the two-frequency-loop model, PI static optimal control is used in the low-frequency-loop, while by using a reduced order fault observer to detect the state of fault and the state of the system at the same time, then adopt a optimal fault-tolerant control, and then maximize the efficiency of captured wind energy, as well as the system work well when the sensors and the actuators are error. Simulation results demonstrate that when the sensors and the actuators are error, the feasibility of two-frequency-loop control based on the optimal fault-tolerant control is effective.